It has long been known that the inside surfaces of a vertical tube or pipe can be cleaned using a high pressure water spray. This is done on a routine basis, for example, in the oil well industry. In general, these methods involve lowering a spray head on the end of a small diameter metal tube. The spray is directed radially in all directions and the velocity of the fluid stream against the wall loosens the materials adhered to the wall.
To enhance the action of the spray, devices were developed wherein the spray head is caused to rotate as shown in U.S. Pat. No. 4,799,554 and U.S. Pat. No. 4,781,250. In these devices, cams and lugs interact to cause the spray head to shift its position vertically and radially. In another patent, U.S. Pat. No. 4,763,728, the spray is also directed radially and a sump is provided to pick up the debris and convey it away. However, none of these existing patents are effective in cleaning both sides of an annulus formed when pipes are concentrically nested and the passage to be cleaned is the inner surface of an outer pipe and the outer surface of an inner pipe as is found in a conventional gravity pressure vessel.
One method of cleaning the annuli in a gravity pressure vessel is described in U.S. Pat. No. 4,594,164. There it is suggested that nitric acid can be introduced, after a conditioning or cooling step, to dissolve away mineral deposits such as calcium sulfate. This results in the need to interrupt production, cool the apparatus, clean the apparatus, and then re-heat the system before going back into production. For a mineral content typical of most waste streams being treated by the gravity pressure vessel, this process may have to be repeated every ten days. As this procedure requires at least a day to complete, it results in a potential loss of ten percent of the operational payback from system operation. Further, not only are such acid washes potentially dangerous to the user, but also they are not completely effective against silicates which have a tendency to gradually accumulate over the life of the gravity pressure vessel. Thus, the unique needs of cleaning the passages in a gravity pressure vessel go unresolved.